1. Field of the Invention
The invention pertains to scan converters and more particularly to scan converters that store airborne radar data north up in an X, Y coordinate system and display this data in an aircraft heading up X, Y coordinate system.
2. Description of the Prior Art
Airborne radar systems, such as that utilized for weather detection have a nose mounted antenna that scan symmetrically about the longitudinal axis of the aircraft. Detected radar returns received in a .rho.-.theta. coordinate system are generally displayed in a X, Y raster, similar to that of a T.V. system. Conventional scan converters for these systems convert the .rho.-.theta. antenna coordinates to store the data in an arranged X-Y coodinate memory. This memory is subsequently readout in synchronism with the raster scan and displayed in X, Y format. The memory has rows and columns with each row and each column representative of X and Y coordinates respectively. In the prior art data is stored in the memory in a heading up mode, for example, north up when the aircraft is heading north, east up when the aircraft is heading east. At each X, Y intersection, a word of memory is stored which is acessed by X, Y address codes. Typically, the memory contains one full antenna scan of information in X, Y coordinates which remains stationary and are displayed numerous times during one antenna scan. In order to provide a heading up display after a turn the entire memory must be rotated to coincide with the new aircraft heading, a task that requires appreciable processing. When the aircraft turns each antenna scan provides the displaced information relative to the proceeding scan and the displayed information jumps each time the memory is updated by an antenna scan. It is desirable to rotate the information in the memory in synchronism with the turning aircraft to provide a continuously moving display, with a minimum of processing time. This may be accomplished by rotating all of the information stored in the memory prior to each raster frame. The large amount of data stored, however, requires inordinate processing times to perform the transformations, thus such systems are extremely complex and expensive.